The present invention relates to oil modified polyurethane-urea dispersions in water and coatings produced therefrom. The present invention represents an improvement in the area of polyurethane dispersion resins and an improvement in the coatings art. The improvement comprises the addition of a modifier composition selected from the group consisting of C6-C22 aliphatic chain-containing anhydride-functional fatty acids and oils, C6-C22 aliphatic chain containing epoxidized oils, and mixtures thereof, to an isocyanate-functional prepolymer. If used in the aqueous phase, the modifier composition is chemically attached to the prepolymer via the diamine chain extender. If used during the prepolymer cook, the modifier composition attaches to the prepolymer backbone via an active-hydrogen containing composition. The resultant polymer exhibits excellent water repellency due to the inclusion of the hydrophobic aliphatic end group. Introducing long hydrophobic end groups imparts excellent water resistance and beading characteristics, even to a low molecular weight dispersion polymer. Such low molecular weight polymers would otherwise be expected to show early water sensitivity.
The polymer is particularly useful as either a surface coating or as a penetrating finish on porous substrates such as wood, concrete, cement, brick and the like. Surface coatings can be very high molecular weight, can be highly crosslinked, and characteristically form a continuous film over the substrate. Varnishes and polyurethane clearcoats are typically classified as surface coatings.
Penetrating finishes, on the other hand, are designed to protect a substrate, and typically change a substrate's color, yet retain the natural textural appearance of the substrate. Penetrating pigmented stains, non-pigmented wood preservatives, and water sealants are typical examples of penetrating finishes. One key attribute of penetrating finishes is that they are designed so as not to form an appreciable surface film or coating on the wood/substrate. They are typically low in molecular weight and very small particle size. They are durable, well suited for textured, exposed surfaces such as siding, decks, steps and the like, can contain water repellants, and are easily applied.
This invention is directed to polyurethane dispersion resins and to both surface coatings and penetrating finishes containing such dispersions.
With the advent of environmental laws and regulations controlling the maximum amounts of VOC permitted in paints, coatings, stains, sealants and the like, numerous attempts have been made in the prior art to formulate coatings and stains which comply with the VOC requirements.
For example, European Patent Application 0 314 378 A1 to Adkins discloses a waterborne alkyd deck stain containing a medium-long oil length water-reducible alkyd resin solubilized in water with the use of propylene glycol tertiary butyl ether as a coupling solvent. Adkins claims to have low VOC, good resistance to water, durability to abrasion and the like.
Likewise, U.S. Pat. No. 4,276,329 to Vasishth et al. discloses a composition for treating and protecting wood surfaces comprising a low molecular weight alkyd resin in a cosolvent of water and glycol ether.
U.S. Pat. No. 4,432,797 to Vasishth et al. discloses a water based thickened stain containing a film forming resin, pigment, thickener and water. The resin is taught to be either an alkyd, a water based acrylic or a water solution of a modified polysaccharide polymer.
UK Patent Application 2 215 732 A to Timperley discloses a water based wood staining composition comprising a water soluble acrylic resin and a pigment.
UK Patent 1 589 605 to Gorivaerk disclose a method of preparing a penetrating wood stain of a suspension of finely divided solids in an oil-in-water emulsion.
U.S. Pat. No. 5,310,780 relates to previous work of one of the present inventors. The present invention represents a substantial improvement over the '780 patent. The improvement comprises the addition of a modifier composition selected from the group consisting of C6-C22 aliphatic chain-containing anhydride-functional fatty acids and oils, C6-C22 aliphatic chain containing epoxidized oils, and mixtures thereof, to an isocyanate-functional prepolymer. The modifier composition is either chemically attached to the prepolymer via the diamine chain extender or to the prepolymer backbone via an active-hydrogen containing prepolymer reactant, resulting in a polymer that exhibits excellent water repellency due to the inclusion of the hydrophobic aliphatic end group.
U.S. Pat. No. 5,354,807 to Dochniak discloses anionic water dispersed polyurethane polymers that comprise the reaction product of a polyisocyanate, an active-hydrogen containing compound such as a polyol and a diamine monomer containing a pendant aliphatic.